Speed of Sound Calculator — Air & Mach Number
The speed of sound in air rises with temperature. Enter the air temperature to get the speed of sound in m/s, km/h, mph and ft/s. Optionally enter an object's speed to compute its Mach number — the ratio of its speed to the local speed of sound.
°C
m/s
Speed of sound in dry air at the given temperature
- 1
Kelvin temperature
20 + 273.15 = 293.15 - 2
Temperature ratio T / 273.15
293.15 ÷ 273.15 = 1.07322 - 3
Square root of ratio
√(1.07322) = 1.035963 - 4
Speed of sound
331.3 × 1.035963 = 343.21
How does this calculator work?
Speed of sound in dry air = 331.3 × √(T_K / 273.15) m/s. At 0 °C: 331.3 m/s; 15 °C (ISA sea level): 340.3 m/s; 20 °C: 343.2 m/s; −50 °C (cruise altitude): ~299 m/s. Mach number = object speed ÷ local sound speed. Sound slows at altitude because temperature decreases.
Formula
How this is calculated
Sound is a longitudinal pressure wave: molecules compress and rarify along the direction of propagation. Its speed depends on how quickly pressure disturbances are restored, which increases with temperature because hotter molecules move faster and transmit the disturbance more readily. The standard formula for dry air is v = 331.3 × √(T/273.15) m/s, where T is absolute temperature in Kelvin (T = T_°C + 273.15). At ISA sea-level conditions (15 °C) the result is about 340.3 m/s; at 20 °C it is 343.2 m/s; at −50 °C (typical jet-cruise altitude) it drops to about 299 m/s.
Humidity has a smaller but real effect: humid air contains water vapour (molar mass 18 g/mol) mixed with dry air (~29 g/mol), making the mixture slightly less dense and raising the sound speed by up to ~0.4 % at 100 % relative humidity and 20 °C. The dry-air formula used here is the dominant factor; for precision acoustic work add about +0.3 m/s per 10 % relative humidity at 20 °C.
The Mach number M = v_object/v_sound classifies flight regimes: subsonic (M < 0.8), transonic (0.8–1.2), supersonic (1.2–5), and hypersonic (M > 5). The sonic boom occurs when an object's shock wave accumulates near Mach 1. Drag rises sharply through the transonic regime. Because air temperature decreases with altitude (ISA lapse rate: −6.5 °C/km up to the tropopause at 11 km), Mach 1 is reached at a lower airspeed at altitude than at sea level.
Frequently asked questions
At the ISA standard sea-level temperature of 15 °C, the speed of sound in dry air is 340.3 m/s (1,225 km/h, 761 mph, Mach 1). At 20 °C it is 343.2 m/s; at 0 °C it is 331.3 m/s.
At altitude, air temperature drops (roughly −6.5 °C per 1,000 m in the ISA model up to 11 km). Lower temperature means slower molecular motion and a slower speed of sound. For an ideal gas the sound speed depends only on temperature — pressure and density have no direct effect.
Yes — much faster. Sound in sea water travels at ~1,480–1,530 m/s; in steel at ~5,050 m/s. Both are much faster than air because water is nearly incompressible and steel is very stiff, so pressure disturbances propagate almost instantly. Use the Speed of Sound in Solids calculator for solid materials.
Also known as
TG we-Calculate Editorial Team. (2026). Speed of Sound Calculator — Air & Mach Number [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/speed-of-sound-calculator
TG we-Calculate Editorial Team. "Speed of Sound Calculator — Air & Mach Number." TG we-Calculate. 2026. https://we-calculate.com/calculator/speed-of-sound-calculator.
TG we-Calculate Editorial Team, "Speed of Sound Calculator — Air & Mach Number," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/speed-of-sound-calculator
@misc{wecalculate_speed_of_sound_calculator, title = {Speed of Sound Calculator — Air & Mach Number}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/speed-of-sound-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?